Figure 2: Defect distributions and detecting near-surface band bending.

(a) Histograms of the Bi_Se defect energies in Cu_xBi₂Se₃, extracted from multipass dI/dV images, show a decreasing gap between the peaks as the Cu content is increased. (b) Schematic of the proposed band-bending mechanism responsible for the energy difference between the defects; the orange profile represents the Bi_Se defect’s observable states on the Bi₂Se₃ surface. Cross-sectional dI/dV linescans from two different defects on Bi₂Se₃ are shown for direct comparison, as well. Colour scale ranges in b: left, 1.4 × 10⁻¹¹ pA meV⁻¹, right, 5.0 × 10⁻¹² pA meV⁻¹.